Field of the Invention
The present invention relates to a radiation imaging apparatus, a method of driving the same, and a radiation imaging system.
Description of the Related Art
A radiation imaging apparatus can include, for example, a pixel array in which a plurality of pixels are arrayed in a matrix and a readout unit which reads out a pixel signal from each pixel. Signal lines (also referred to as column signal lines) corresponding to columns are arranged on the pixel array, and each pixel can include, for example, a detecting element which detects radiation and a switch element which connects the detecting element with a corresponding signal line. When the switch element is changed to a conductive state, a pixel signal is read out by the readout unit via a corresponding signal line.
Among radiation imaging apparatuses, there is an apparatus that requests the end of radiation irradiation (for example, generates a signal to end radiation irradiation) in accordance with the radiation irradiation amount reaching a reference value. Such control is called auto exposure control (AEC). In Japanese Patent Laid-Open No. 2012-15913 (paragraph 0094), some of the plurality of pixels are driven in a predetermined cycle to read out pixel signals, and AEC is performed based on the readout signal values.
Each signal read out by the readout unit contains an offset component which is a type of noise. The offset component corresponds to the potential of the signal line when each pixel signal is not being read out (that is, when the switch element is in a non-conductive state) or the output value of the readout unit corresponding to the potential. The offset component can decrease the accuracy of AEC. Here, to prevent the decrease in the accuracy of AEC, a method of performing AEC based on a difference between the offset component obtained by changing the switch elements to the non-conductive state and the pixel signals obtained by changing the switch elements to the conductive state can be considered.
However, the offset component may change before and after the switch elements are changed to the conductive state. Hence, it is difficult to prevent the accuracy of AEC from decreasing if AEC is performed simply based on the difference between the offset component and the pixel signals.